This invention relates to internal combustion engines and, more particularly, to the provision of an improved expansion cycle stroke characteristic in an internal combustion engine.
A form of the internal combustion engine, generally used for powering automobiles, operates in accordance with the Otto cycle, and may be referred to herein as a gasoline engine, as distinguished from a diesel engine. The gasoline engine employs one or more cylinders, each cylinder having a piston movable therein with reciprocating motion for the driving of a crankshaft of the engine. Output power of the engine, for the driving of a load, is obtained from the rotating crankshaft. In the four-stroke form of the gasoline engine, the movement of a piston in its cylinder is characterized by four strokes, which occur in a repeating sequence, the sequence of the four strokes being; an induction stroke, a compression stroke, a power (or expansion) stroke, and an exhaust stroke. During the induction stroke, the piston moves away from the head of the cylinder to produce a vacuum which draws in a mixture of air and fuel vapors via an intake valve generally located in the head of the cylinder. During the compression stroke, the piston moves towards the cylinder head to compress the air-fuel mixture. Approximately at the beginning of the power stroke, there is ignition of the air-fuel mixture and, during the power stroke, the expanding gases produced by the combustion of the fuel drive the piston away from the cylinder head. During the exhaust stroke, the piston moves towards the cylinder head to drive the exhaust gases out of the cylinder via an exhaust valve generally located in the cylinder head. In the usual construction of such an engine, an intake manifold is provided for bringing air and fuel from a carburetor or fuel-injection assembly to the intake ports of the cylinders, and an exhaust manifold is provided for removal of combustion gases via exhaust ports of the cylinders.
It is useful to compare operation of the gasoline engine with the diesel engine. In the case of the gasoline engine, both fuel and air are present in the cylinder during the compression stroke. The temperature produced in the gases within the cylinder is below the ignition temperature of the air-fuel mixture so as to avoid premature ignition of the air-fuel mixture. Ignition is produced by an electric spark of a spark plug, mounted within the cylinder head. In a modem engine, activation of the spark plug at an optimum moment, relative to the time of occurrence of the power stroke, is provided by a computer. In the case of the diesel engine, only the air is present in the cylinder during the compression stroke. The geometry of the piston within the cylinder of the diesel engine differs somewhat from the corresponding geometry of the gasoline engine such that the compression stroke of the diesel engine provides significantly more compression of the gases within the cylinder (a compression ratio of approximately 15:1) than occurs in the gasoline engine (a compression ratio of approximately 8:1). As a result, in the diesel engine, the temperature of the air is raised by the compression stroke to a temperature high enough to ignite fuel. Accordingly, in the diesel engine, the fuel is injected into the cylinder at approximately the beginning of the power stroke, and is ignited by the high air temperature.
It is observed furthermore, that in the usual construction of a gasoline engine and of a diesel engine, the ratio of the expansion of the volume of cylinder gases, final volume divided by initial volume of the power stroke, is equal to the ratio of the compression of the volume of the cylinder gases, initial volume divided by final volume of the compression stroke. By way of example for a gasoline engine, compression and expansion is characterized by a ratio of approximately 8:1, and for a diesel engine, compression and expansion is characterized by a ratio of approximately 15:1. The expansion of the cylinder gases in the power stroke is accompanied by a reduction in the temperature of the cylinder gases. Well-known theoretical considerations show that an important consideration in determining the efficiency of the engine is the ratio of the gas temperature at the beginning of the power stroke to the gas temperature at the end of the power stroke. A greater temperature ratio is obtained in the case of the diesel engine than for the gasoline engine. This is one of the reasons that the diesel engine can operate more efficiently than the gasoline engine.
Based on the foregoing theoretical consideration, it appears that there would be an advantage to the construction of a gasoline engine with a higher, or elevated, expansion ratio of the power stroke without a corresponding increase in the compression ratio of the compression stroke. By maintaining the relatively low value of the compression ratio in the compression stroke, the temperature of the cylinder gases would be maintained at a sufficiently low value so as to avoid premature ignition, as in present-day gasoline engines, while greater efficiency would be obtained as in present-day diesel engines. A further advantage of such an engine would be the avoidance of needless excess compression during the compression stroke, a matter which can be appreciated by one attempting to start an engine by hand.
Such a construction of an elevated expansion-ratio engine would be advantageous for the form of the internal combustion engine, generally used for powering automobiles, that operates in accordance with the Otto cycle, as well as other “mixed ” cycle four stroke-repeating internal combustion engines. Such a construction of an elevated expansion-ratio engine would be advantageous also for a diesel engine wherein an expansion ratio in the power stroke of 20:1, by way of example, could be obtained for still greater efficiency while the compression ratio of the compression stroke would be maintained at 15:1. However, attempts to build such an engine have not met with commercial success.